Studies of prototype DEPFET sensors for the Wide Field Imager of Athena

摘要

The Wide Field Imager (WFI) of ESA's next X-ray observatory Athena will combine a high count rate capability with a large field of view, both with a state-of-the-art spectroscopic performance. To meet these demands, specific DEPFET active pixel detectors have been developed and operated. Due to the intrinsic amplification of detected signals they are best suited to achieve a high speed and low noise performance. In the course of the development of the DEPFET sensors, different fabrication technologies and transistor geometries have been implemented on a dedicated prototype production. The main modifications between the sensors concern the shape of the transistor gate - regarding the layout - and the thickness of the gate oxide - regarding the technology. To facilitate the fabrication and testing of a large variety of sensors the presented studies were carried out with 64×64 pixel detectors. The detector comprises a control ASIC (Switcher-A), a readout ASIC (VERITAS-2) and the sensor. In this paper we give an overview on the evaluation of different prototype sensors. The most important results, which have been decisive for the identification of the optimal fabrication technology and transistor layout for subsequent sensor productions are summarized. It will be shown that the developments result in an excellent performance of spectroscopic X-ray DEPFETs with typical noise values below 2.5 ENC at 2.5 μs/row